Have you ever wondered which animals learn to communicate with sounds and how? We can precisely control our vocal tract and vocal cords when learning new sounds. But the capacity for ‘vocal learning’ is extremely rare; fewer than 100 attested species with only a dozen mammals are capable of learning how to produce sounds for communication. For example, cats, dogs and chimpanzees cannot learn vocalizations. Amanda Stansbury and Vincent Janik from the University of St Andrews, UK, tested whether grey seals (Halichoerus grypus) can be trained to learn new sounds by imitation.
The researchers trained a grey seal, named Zola, to copy three sounds played through a loudspeaker. To make the task easier for Zola, these sounds were recordings of her own calls, which had been shifted in frequency to sound higher or lower. Every time Zola reproduced one of the sounds at the correct pitch, she received a fish reward. After training, Zola could copy sequences of up to 10 sounds varying in pitch, most of which she had not heard before. However, when the team analysed the audio recordings, they discovered that instead of modifying the vibration frequency of her vocal folds – as humans do when singing – Zola was altering the shape of her vocal tract, similar to the way we change the shape of our mouths when going from ‘bath’ to ‘boot’. She could even imitate motifs such as the ‘Star Wars’ theme and ‘Twinkle little star’; the videos are a must-watch. So, Zola the ‘singing seal’ could imitate tunes by performing vocal tract movements that we humans usually make when speaking.
Stansbury and Janik then trained two more seals, Janice and Gandalf, to imitate five vowel sounds – similar to those found in (British English) ‘bath’, ‘may’, ‘meet’, ‘thought’ and ‘boot’ – to assess the animals’ ability to control their vocal tracts. To make the task more manageable, Stansbury and Janik produced the vowel sounds by modifying the seals’ own calls and trained Janice and Gandalf to match these modified calls. Eventually, both seals could reliably imitate the five vowels by emphasizing either the lower or higher frequencies. The seals had changed their voices to sound deeper (as in ‘boot’) or more acute (as in ‘meet’), so that they no longer sounded like other seals. They had learned how to produce new sounds instead of ‘recycling’ sounds they could already produce.
Why is this story scientifically interesting? Stansbury and Janik provide experimental evidence that it is possible for some mammals other than humans to learn to produce new sounds via modifications of their vocal tracts. This is something we humans do constantly when learning our mother tongue or a new language. Currently, many researchers study bird song production to help us understand human speech, but now a much closer relative – seals, with their human-like vocal tracts and learning abilities – could be a perfect alternative model species for learning about human speech and song thanks to our similar anatomy. In addition, it is possible to measure the brain activity of seals, potentially allowing us to identify which areas of the brain are key for seal vocal imitation.
In brief, seals may have much to teach us about human speech and song. Seal scientists are beginning to listen and you are all welcome to join in too.